Variable Output Heating Control System

ABSTRACT

A variable output heating control system includes a user interface, an operating parameter sensor, a controller, a combination control valve, a plurality of variable flow valves and a plurality of burners. The user interface allows a user to enter operating parameters, such as a set temperature. The operating parameters sensor provides measured parameters, such as a measured temperature. The controller receives the set temperature and the measured temperature and generates commands to control the flow of gas based on the set temperature and the measured temperature. The combination control valve shuts off the flow of gas from an external gas source based on a command from the controller. The plurality of variable flow valves vary the flow of gas that is received from the combination control valve. The plurality of burners provides heat based on the combustion of gas that is received from the plurality of variable flow valves.

RELATED APPLICATION

This application is a Continuation application and claims prioritybenefit, with regard to all common subject matter, of earlier-filed U.S.nonprovisional patent application titled “VARIABLE OUTPUT HEATINGCONTROL SYSTEM”, Ser. No. 12/167,723, filed Jul. 3, 2008. U.S. patentapplication Ser. No. 12/167,723, being of common ownership herewith, isincorporated herein by reference in its entirety into the presentapplication to provide continuity of disclosure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to systems and methods forcontrolling combustible fuel heating systems. More particularly,embodiments of the present invention relate to systems and methods forcontrolling gas flow to individual or multiple burners in a combustiblefuel heating system.

2. Description of the Related Art

Residential and commercial gas furnace systems typically employ multipleburners to provide sufficient heating capacity. Generally, a combinationcontrol valve controls the supply of fuel from a fuel source to theburners in an on/off fashion, such that all the burners are either fullyon or fully off. The furnace cannot turn on individual burners nor canit vary the flow of gas to the burners. This type of on/off controlsystem often incurs temperature overshoot, wherein the outputtemperature (or the ambient temperature of the house or building) risesabove the temperature setting as a result of all burners turning on atmaximum capacity in an attempt to raise the temperature by a smallamount. Thus, fine resolution control of the output temperature isdifficult. Alternatively, if the control system is adjusted to reducetemperature overshoot, then there is often a large steady-state error ofthe output temperature as compared with the set temperature, typicallyon the cold side, as the control system waits until the outputtemperature drops low enough below the set temperature to turn on allthe burners at maximum capacity. Therefore, the on/off heating controlsystem is inefficient by using excessive energy to maintain the settemperature or is ineffective by leaving the burners off for too longresulting in a cold and uncomfortable environment.

SUMMARY OF THE INVENTION

Embodiments of the present invention solve the above-mentioned problemsand provide a distinct advance in the art of controlling the flow of gasin a gas furnace. More particularly, embodiments of the inventionprovide a system and method for varying or shutting off the flow of gasto individual burners in a multiple-burner combustible fuel heatingsystem.

In various embodiments, the system may comprise a user interface, anoperating parameter sensor, a controller, a plurality of burners, acombination control valve, and a plurality of variable flow valves. Theuser interface may allow a user to enter data, such as a settemperature, into the controller, and to read out information from thecontroller about the status of the system, among other things. Theoperating parameter sensor may measure the ambient temperature of thespace to be heated or the temperature of a particular portion of thesystem. The controller may receive the set temperature from the userinterface and the measured temperature from the operating parametersensor. Based upon the set temperature and the measured temperature, thecontroller may generate a plurality of commands to vary the flow of gasin the system. The combination control valve may control the flow of gasfrom an outside gas source to the plurality of variable flow valves.Generally, the combination control valve is open to allow gas flow or isclosed to prevent gas flow, based upon a command from the controller.The variable flow valves vary the amount of gas flowing from thecombination control valve that is supplied to the burners. The varyingof the gas flow rate is controlled by a command from the controller. Theburners provide combustion of the gas from the variable flow valves,which in turn provides heat.

In other embodiments, the system may comprise a user interface, anoperating parameter sensor, a controller, a plurality of burners, amodulating combination control valve, and a plurality of shutoff valves.The user interface may allow a user to enter data, such as a settemperature, into the controller, and to read out information from thecontroller about the status of the system, among other things. Theoperating parameter sensor may measure the ambient temperature or thetemperature of a particular portion of the system. The controller mayreceive the set temperature from the user interface and the measuredtemperature from the operating parameter sensor. Based upon the settemperature and the measured temperature, the controller may generate aplurality of commands to vary the flow of gas in the system. Themodulating combination control valve may vary the flow of gas from anoutside gas source to the plurality of shutoff valves. The amount bywhich the flow of gas varies is controlled by a command from thecontroller. The shutoff valves control the amount of gas flowing fromthe modulating combination control valve that is supplied to theburners. Generally, the shutoff valve is open to allow gas flow or isclosed to prevent gas flow. The burners provide combustion of the gasfrom the shutoff valves, which in turn provides heat.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

Other aspects and advantages of the present invention will be apparentfrom the following detailed description of the embodiments and theaccompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the present invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a schematic diagram of a variable output heating controlsystem constructed in accordance with a first embodiment of the presentinvention;

FIG. 2 is a schematic diagram of a second embodiment of the variableoutput heating control system;

FIG. 3 is a schematic diagram of a third embodiment of the variableoutput heating control system;

FIG. 4 is a schematic diagram of a fourth embodiment of the variableoutput heating control system; and

FIG. 5 is a schematic diagram of a fifth embodiment of the variableoutput heating control system.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description of the invention references theaccompanying drawings that illustrate specific embodiments in which theinvention can be practiced. The embodiments are intended to describeaspects of the invention in sufficient detail to enable those skilled inthe art to practice the invention. Other embodiments can be utilized andchanges can be made without departing from the scope of the presentinvention. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

A variable output heating control system 10 constructed in accordancewith an exemplary embodiment of the present invention is shown inFIG. 1. The system 10 may comprise a user interface 12, an operatingparameter sensor 14, a controller 16, a heat generating unit 18 thatincludes a plurality of burners 20, a combination control valve 22, anda plurality of variable flow valves 24.

The user interface 12 generally allows a user to interact with thesystem 10, whereby the user may input parameters, commands, and/or dataas well as obtain information from the system 10, and in particular, thecontroller 16. The user may utilize the user interface 12 to input datasuch as a desired temperature setting or a range of temperaturesettings. The user may also use the user interface 12 to program asequence of temperatures based on time of day, day of week, or othercriteria. For example, the user may program a certain temperature ortemperatures for the daytime hours and a different set of temperaturesfor the nighttime hours. The user may also program a particular sequenceof temperatures for the week days and a different sequence for theweekends. The user may enter other parameters as well, such as a gaspressure or a gas flow rate. In addition, the user may enter commandsvia the user interface 12. The user may power the system 10 on or off ormay control auxiliary devices, such as a fan or blower. Furthermore, theuser may utilize the user interface 12 to view data or commands as theyare being entered, as well as review the status or settings of thesystem 10 and programmed temperature sequences.

The user interface 12 may include data entry devices such astouchscreens, keyboards, keypads, mice or other pointing devices,pushbuttons, switches, rotary knobs, and the like. The user interface 12may also include data readout devices such as monitors (e.g., cathoderay tube (CRT), plasma, liquid crystal display (LCD)), dot-matrixdisplays, seven-segment LED displays, one or more individual LEDs orlights, and the like. The user interface 12 may include other electricalor electronic components formed from analog and digital circuitry, suchas analog-to-digital converters (ADCs) or digital-to-analog converters(DACs), and the like.

The data entry and data readout portions of the user interface 12 may beintegrated in a single unit or may be housed in separate units. The userinterface 12 may be located in close proximity to the rest of the system10 and in some embodiments the user interface 12 may be integrated withthe controller 16. In other embodiments, the user interface 12 may beremote from the controller 16 and the heat generating unit 18, such asin another room or another building. The user interface 12 maycommunicate with the controller 16 either via wires or wirelessly. Thewires may include commonly-known metallic conductors such as individualwires or multi-conductor cables, optical fibers, or other physicalcommunication media. Wireless communication may include radio frequency(RF) transmission that utilizes standard analog or digital protocols,such as Institute of Electrical and Electronics Engineers (IEEE)wireless standards 802.11, 802.15 (which includes Bluetooth™), 802.16,and the like. Wireless communication may also include optical line ofsight transmission, or similar wireless communication methods.

The operating parameter sensor 14 generally senses or measures aplurality of operating parameters and reports them to the controller 16.The controller 16 may adjust the settings of the combination controlvalve 22 and the variable flow valves 24 based on data from theoperating parameter sensor 14. Parameters that the operating parametersensor 14 is capable of measuring may include thermal energy, or ambienttemperature, gas pressure, or gas flow rate. Typically, the operatingparameter sensor 14 is located in a room or area of primary importance,perhaps where people spend most of their time. Often, the operatingparameter sensor 14 is located in a central portion of the home orbuilding, which may also be the location of the controller 16 and insome embodiments, the operating parameter sensor 14 may be integratedwith the controller 16. The system 10 may also include more than oneoperating parameter sensor 14 to sense parameters in various locations,such as different rooms or different levels of a house or building. Thecontroller 16 may average the readings from the different operatingparameter sensors 14 or may apply a different criteria or algorithm whendetermining how to set the valves based on temperature, pressure, orflow readings. In various embodiments, there may also be one or moreoperating parameter sensors 14 positioned near the burners 20 and in oraround the combination control valve 22 and the variable flow valves 24to detect the performance of the heat generating unit 18. Theseoperating parameter sensors 14 may monitor the temperature, pressure, orflow rate among components such as a heat exchanger, duct inlets, andduct outlets.

The operating parameter sensor 14 may include devices to measure thermalenergy, such as thermometers, infrared sensors, thermal transducers, gaspressure sensors or transducers, gas flow meters, and the like. Theoperating parameter sensor 14 may also include other electrical orelectronic components formed from analog and digital circuitry, such asADCs or DACs, and the like.

As with the user interface 12, the operating parameter sensor 14 maycommunicate with the controller 16 either via wires or wirelessly. Thewires may include commonly-known metallic conductors such as individualwires or multi-conductor cables, optical fibers, or other physicalcommunication media. Wireless communication may include RF transmissionthat utilizes standard analog or digital protocols, such as IEEE 802.11,802.15, 802.16, and the like. Wireless communication may also includeoptical line of sight transmission, or similar wireless communicationmethods.

The controller 16 generally receives input from the user interface 12and the operating parameter sensor 14 and transmits output to the userinterface 12, the combination control valve 22, and the variable flowvalves 24. The controller 16 may receive input from the user interface12, such as a desired temperature setting (set temperature), and fromthe operating parameter sensor 14, such as a measured temperature, bothas described above. Based on the set temperature, the measuredtemperature, and the temperature difference (being the set temperatureminus the measured temperature), the controller 16 may send signals tothe combination control valve 22 and the variable flow valves 24 toeither increase or decrease the flow of gas to the burners 20.Generally, the flow of gas is proportional to the temperaturedifference. The greater the temperature difference, the greater the flowof gas. The smaller the temperature difference, the smaller the flow ofgas.

The system 10 generally matches the architecture of a feedback controlsystem 10 with an input to the system 10 being the set temperature fromthe user interface 12, the controlled quantity being heat (as producedby combustion of flowing gas), and feedback of the controlled quantitybeing the measured temperature supplied by the operating parametersensor 14. As such, the controller 16 may include one or more generallyknown control structures, such as a proportional-integral-derivative(PID) controller, or variations thereof. The controller 16 may also bedesigned for optimization, such as minimizing temperature overshoot,response time, settling time, steady-state error, or other criteria.

The controller 16 may be implemented in hardware, software, firmware, orcombinations thereof. The controller 16 may include a processing elementcoupled with a memory element that in combination are able to executesoftware code segments which implement the control function. Thecontroller 16 may also include microcomputers, microprocessors,microcontrollers, programmable intelligent computers (PICs),field-programmable gate arrays (FPGAs), programmable logic devices(PLDs), programmable logic controllers (PLCs), and the like. Thecontroller 16 may also include a requisite memory component such ashard-disk drives, optical disks, floppy disks, random-access memory(RAM), read-only memory (ROM), cache memory, programmable ROM (PROM),erasable PROM (EPROM), and the like. Furthermore, the controller 16 mayinclude actuating components that are capable of receiving a temperaturevariable signal, wherein the components may be pneumatic, hydraulic,bimetallic, or the like.

The controller 16 may be located in the proximity of the heat generatingunit 18, or may be remote from the heat generating unit 18, and furthermay be integrated with the user interface 12, the operating parametersensor 14, or both. Similar to the components described above, thecontroller 16 may communicate with the combination control valve 22 andthe variable flow valves 24 either via wires or wirelessly. The wiresmay include commonly-known metallic conductors such as individual wiresor multi-conductor cables, optical fibers, or other physicalcommunication media. Wireless communication may include RF transmissionthat utilizes standard analog or digital protocols, such as IEEE 802.11.Wireless communication may also include optical line of sighttransmission, or similar wireless communication methods.

The combination control valve 22 generally reduces the pressure of thegas coming from an external supply that is delivered through a gas inlet26. The reduced pressure gas may be in turn supplied to the variableflow valves 24, which control the flow of gas to the burners 20. Thecombination control valve 22 may also shut off the supply of gas to thevariable flow valves 24. The operation of the combination control valve22 may be determined by the controller 16, such that the controller 16may send a signal to the combination control valve 22 to close and shutoff the supply of gas to the variable flow valves 24.

The combination control valve 22 may include components for the controlof gas flow such as a gas pressure regulator, a pilot valve, an ignitionsource, a flame sensor, and a safety shutoff valve. The gas pressureregulator may regulate the pressure of the gas delivered to the variableflow valves 24 at a constant value in order to maintain consistency ofthe heating rate of the system 10.

The combination control valve 22 and the variable flow valve 24 may begenerally in close proximity to each other. The combination controlvalve 22 may be connected to the variable flow valves 24 through amanifold 28. Other connection schemes include piping, tubing, ducting,or the like, in addition to fittings, connectors, and couplers.

The variable flow valve 24 generally modulates the flow of gas to theburner 20 to which it is coupled. An example of the variable flow valve24 is disclosed in “VARIABLE ORIFICE GAS FLOW MODULATING VALVE”,application Ser. No. 11/751,854, filed May 22, 2007, which, being ofcommon ownership, is hereby incorporated by reference, in its entirety.The variable orifice modulating valve of application Ser. No. 11/751,854controls the flow of gas by the movement of a metering pin at the outputorifice. However, other valves that can vary the flow of gas through anoutput may be used for the variable flow valve.

Generally, the variable flow valve 24 may be able to modulate the flowof gas in incremental steps of 1% or less. Thus, the variable flow valve24 may allow the rate of gas flowing to the burner 20 to vary from 100%down to less than 1%. The variable flow rate of the variable flow valve24 may be controlled by a signal from the controller 16. The variableflow valve 24 may receive gas from the combination control valve 22through the manifold 28 and may supply regulated-flow gas to the burner20 through an output orifice 30 at one end of the variable flow valve24.

The burner 20 may include an inlet port 32, a mixing chamber 34, and aplurality of outlet ports 36. The burner 20 may be somewhat elongated,though other shapes are possible. At one end may be the inlet port 32,through which the burner 20 receives gas from the output orifice 30 ofthe variable flow valve. There may also be a gap between the outputorifice 30 of the variable flow valve 24 and the inlet port 32 throughwhich ambient air flows. The flow of gas into the inlet port 32generally pulls in ambient air into the mixing chamber 34, where gas andambient air combine. The amount of air in the mixing chamber 34 may berelated to the velocity of the flow of gas from the output orifice 30.The greater the velocity of gas flow, the more air that is in thechamber, wherein a sufficient amount of air is desirable to provide morethorough combustion of the gas. Thorough combustion of the gas generallyincreases the efficiency of the system 10 and reduces the emission ofuncombusted gas into the atmosphere. The output orifice 30 of thevariable orifice modulating valve described above generally provides gasflow at a higher velocity, which in turn helps pull in a sufficientamount of air to the mixing chamber 34. The outlet ports 36 may beuniformly distributed along the length of the burner 20 and may provideflames 38 as a result of the combustion of the gas and air mixture. Thelevel of the flames 38 may also be directly related to the amount ofheat given off by the burner, such that higher flames 38 may relate togreater heat being produced.

The burner 20 may also include one or more of the following components:atmospheric burners, induced draft burners, power burners, or inshotburners. Power burners and induced draft burners may utilize an electricpowered blower to supply primary air to the burner 20 for mixing withthe gas flow, to create the desired gas and air ratio for completecombustion. Alternatively, atmospheric type burners rely on the flowvelocity of the gas exiting the orifice to create enough draft in themixing chamber 34 area of the burner 20 to draw in sufficient primaryair for complete combustion. Furthermore, the burner 20 may include aturndown ratio, which establishes the lower limit of the gas flow ratethat the burner 20 is capable of supporting. For example, a burner 20with a 4:1 turndown ratio may support a gas flow rate of 25%, orgreater, of maximum flow rate. In this example, a gas flow rate of below25% may result in decreased energy efficiency and increased emissions ofuncombusted gas.

The variable output heating control system 10 may operate as follows.The system 10 may include one or more burners 20 and variable flowvalves 24. An exemplary embodiment of the system 10, as seen in FIG. 1,includes five burners 20 receiving gas from five variable flow valves24. A user enters a temperature, the set temperature, to the controller16 by using the user interface 12. The user may also enter a “start” orother initiating command to alert the controller 16 that data entry hasceased. The controller 16 compares the set temperature with the measuredtemperature, supplied by the operating parameter sensor 14. If themeasured temperature is above the set temperature, the controller 16 mayclose the combination control valve 22, thereby shutting off the flow ofgas to the variable flow valves 24, and in turn the burners 20. Thecontroller 16 may also send a signal to one or more of the variable flowvalves 24 to reduce the flow of gas to the burners 20 to its minimum orclose to its minimum, thereby reducing the level of the flames 38 andthe heat produced.

If the measured temperature is below the set temperature, the controller16 may send a signal to the combination control valve 22 to open and maysend a signal to one or more of the variable flow valves 24 to open atleast partially to allow some gas to flow to the burners 20, where itmay be combusted and produce heat. If the measured temperature is wellbelow the set temperature, the controller 16 may leave the combinationcontrol valve 22 open and send a signal to one or more of the variableflow valves 24 to allow 100% gas flow to the burners 20, increasing thelevel of the flames 38 and the heat produced. As the measuredtemperature approaches the set temperature, the controller 16 may send asignal to one or more of the variable flow valves 24 to reduce the gasflow rate. For example, the controller 16 may send a signal to all thevariable flow valves 24 to reduce the flow of gas to 50%, therebyreducing the heat output by approximately 50%. However, specifically howeach variable flow valve 24 is controlled (i.e., the value of each flowrate) may depend on a plurality of factors such as the rate at which themeasured temperature is approaching the set temperature as well as thecontroller architecture type and factors that include optimization, suchas reduced temperature overshoot, decreased settling time, etc.

As the measured temperature gets very close to the set temperature, thecontroller 16 may continue to reduce the flow rate of one or more of thevariable flow valves 24. If the measured temperature equals the settemperature, the controller 16 may reduce the flow rate of one or moreof the variable flow valves 24 to its minimum or near the minimum. Thecontroller 16 may maintain this setting, or may adjust the settingslightly, as long as the two temperatures are equal. If the measuredtemperature increases or decreases, the controller 16 may adjust theflow rates of the variable flow valves 24 or open or close thecombination control valve 22 accordingly, as described above.

Another exemplary embodiment of the variable output heating controlsystem 10 is shown in FIG. 2. The system 10 comprises a user interface12, an operating parameter sensor 14, a controller 16, and a heatgenerating unit 18 that includes a plurality of burners 20, a modulatingcombination control valve 40, and a plurality of shutoff valves 42.

The user interface 12, the operating parameter sensor 14, the controller16, and the burners 20 are substantially similar to the same-namedcomponents described above. Additionally, the controller 16 maycommunicate with the modulating combination control valve 40 in the samemanner as the controller 16 may communicate with the combination controlvalve 22 described above. Furthermore, the controller 16 may communicatewith the shutoff valves 42 in the same manner as the controller 16 maycommunicate with the variable flow valves 24 described above.

The modulating combination control valve 40 generally controls the flowof gas from an external fuel supply through the gas inlet 26 to theshutoff valves 42. Typically, the gas coming through the gas inlet 26 isat a relatively high pressure. The modulating combination control valve40 may reduce the pressure of the incoming gas, thereby reducing theflow of gas to the shutoff valves 42. Typically, the modulatingcombination control valve 40 includes all the components of thecombination control valve with additional components or structure thatmay vary, meter, or modulate the pressure of the gas, and in turn theflow of gas, that is supplied to the shutoff valves 42. Furthermore, themodulating combination control valve 40 may cut off the flow of gas tothe shutoff valves 42.

The controller 16 may send a signal to the modulating combinationcontrol valve 40 to set the pressure of the gas supplied to the shutoffvalves 42, wherein the pressure may vary from a level that is below theexternal supply line pressure down to a minimum flow rate that is basedon the burner 20 turndown ratio as described above. The controller 16may also send a signal to the modulating combination control valve 40 toclose and shut off the flow of gas.

The modulating combination control valve 40 and the shutoff valves 42may be generally in close proximity to each other. The modulatingcombination control valve 40 may be connected to the shutoff valves 42through a manifold 28. Other connection schemes include piping, tubing,ducting, or the like, in addition to fittings, connectors, and couplers.

The shutoff valve 42 generally acts as a gate for the flow of gas fromthe modulating combination control valve 40 to the burner 20 to whichthe shutoff valve 42 is coupled. The shutoff valve 42 may be open toallow gas to flow to the burner 20 with little loss of pressure or theshutoff valve 42 may be closed to prevent the flow of gas into theburner 20. The shutoff valve 42 may receive a signal from the controller16 to open and allow gas flow to the burner 20 or to close and preventgas flow to the burner 20. The shutoff valve 42 may include anycomponent or combination of components that is operable to shut off theflow of gas between an input and an output.

The shutoff valve 42 may include an output orifice 30 that is similar tothe output orifice 30 of the variable flow valve 24 and may couple tothe burner 20 in the same manner as the variable flow valve 24,described above.

The operation of the second embodiment of the variable output heatingcontrol system 10 may be as follows. The second embodiment of the system10 may include five burners 20 receiving gas flow from five shutoffvalves 42, as seen in FIG. 2. In a similar fashion to the firstembodiment, discussed above, a user enters the set temperature to thecontroller 16 by using the user interface 12. The controller 16 comparesthe set temperature with the measured temperature. If the measuredtemperature is above the set temperature, the controller 16 may send asignal to the modulating combination control valve 40 to partially closeto reduce the flow of gas to near a minimum flow rate dependent oncomplete combustion of the burners 20 to which it is coupled. Or, thecontroller 16 may close the modulating combination control valve 40,thereby shutting off the flow of gas to the shutoff valves 42. Thecontroller 16 may also send a signal to one or more of the shutoffvalves 42 to stop the flow of gas to each individual burner 20.

If the measured temperature is below the set temperature, the controller16 may send a signal to open at least one of the shutoff valves 42 andto at least partially open the modulating combination control valve 40.If the measured temperature is well below the set temperature, thecontroller 16 may leave the shutoff valves 42 open and send a signal tothe modulating combination control valve 40 to allow 100% gas flow tothe shutoff valves 42, increasing the level of the flames 38 and theheat produced. As the measured temperature approaches the settemperature, the controller 16 may send a signal to the modulatingcombination control valve 40 to reduce the gas flow rate. For example,the controller 16 may send a signal to the modulating combinationcontrol valve 40 to reduce the flow of gas to 50%, thereby reducing theheat output by approximately 50%.

Alternatively, the controller 16 may send a signal to one or more of theshutoff valves 42 to close, without reducing the flow of gas from themodulating combination control valve 40. For example, the controller 16may close two of the five shutoff valves 42, thereby decreasing heatoutput to approximately 60% of full capacity. Furthermore, thecontroller 16 may send a signal to one or more of the shutoff valves 42to close, in addition to sending a signal to the modulating combinationcontrol valve 40 to reduce the flow of gas. For example, the controller16 may close two of the five shutoff valves 42 and reduce the gas flowrate to 50%, thus leaving three burners 20 on, each receiving 50% gasflow rate, thereby reducing heat output to approximately 30% of fullvalue. As with the first embodiment discussed above, how many shutoffvalves 42 are closed and how the flow rate is reduced may depend on aplurality of factors such as the rate at which the measured temperatureis approaching the set temperature as well as the controllerarchitecture type and factors that include optimization, such as reducedtemperature overshoot, decreased settling time, etc.

As the measured temperature gets very close to the set temperature, thecontroller 16 may continue to reduce the flow rate of the modulatingcombination control valve 40, in addition to closing shutoff valves 42as necessary. If the measured temperature equals the set temperature,the controller 16 may reduce the flow rate of the modulating combinationcontrol valve 40 to its minimum or near the minimum, in addition toclosing shutoff valves 42. Although, as long as the modulatingcombination control valve 40 is allowing gas to flow, even at a minimumrate, at least one shutoff valve 42 is open to allow the gas to flow toat least one burner 20. With the combination of reducing gas flow andshutting off burners 20, the controller 16 can adjust the heat output ofthe system 10 with fine resolution. The controller 16 may maintain thissetting, or may adjust the setting slightly, as long as the twotemperatures are equal. If the measured temperature increases ordecreases, the controller 16 may adjust the flow rate of the modulatingcombination control valve 40 or open or close the shutoff valves 42accordingly, as described above.

Another exemplary embodiment of the variable output heating controlsystem 10 is shown in FIG. 3. The third embodiment may comprise a userinterface 12, an operating parameter sensor 14, a controller 16, aplurality of burners 20, a combination control valve 22, and a pluralityof variable flow valves 24. The third embodiment of the system 10 issubstantially similar to the system 10 of the first embodiment excepteach variable flow valve 24 may be coupled to one or more burners 20, asdepicted. The output orifice 30 of each variable flow valve 24 may becoupled to tubing which connects to the inlet port 32 of one or moreburners 20. This embodiment allows for good control of the heat outputwhile offering reduced cost of manufacture by reducing the number ofvariable flow valves 24 needed for a given number of burners 20.

Another exemplary embodiment of the variable output heating controlsystem 10 is shown in FIG. 4. The system 10 of the fourth embodiment maycomprise a user interface 12, an operating parameter sensor 14, acontroller 16, a plurality of burners 20, a modulating combinationcontrol valve 40, and a plurality of shutoff valves 42. The fourthembodiment of the system 10 is substantially similar to the system 10 ofthe second embodiment except each shutoff valve 42 may be coupled to oneor more burners 20, as depicted. The output orifice 30 of each shutoffvalve 42 may be coupled to tubing which connects to the inlet port 32 ofone or more burners 20. This embodiment allows for good control of theheat output while offering reduced cost of manufacture by reducing thenumber of shutoff valves 42 needed for a given number of burners 20.

Another exemplary embodiment of the variable output heating controlsystem 10 is shown in FIG. 5. The system 10 of the fifth embodiment maycomprise a user interface 12, an operating parameter sensor 14, acontroller 16, a plurality of burners 20, a combination control valve22, and a shutoff valve 42. These components operate in a substantiallysimilar fashion as described above. The combination control valve 22controls the flow of gas to a plurality of burners 20 through a standardorifice 44. Thus, the combination control valve 22 may shut off the flowof gas to the burners 20. The shutoff valve 42 may be coupled to atleast one of the burners 20, as depicted in FIG. 5, allowing the abilityto shut off the flow of gas to only those burners 20 coupled to ashutoff valve 42. This embodiment of the system 10 can providetemperature control by shutting off one or more selected burners withoutadding modulation controls, which may be more expensive.

The variable output heating control system 10 of the fifth embodimentmay operate as follows. The system 10 may include one or more burners20, the combination control valve 22, and at least one shutoff valve 42.An exemplary embodiment of the system 10, as seen in FIG. 5, includesfour burners 20 receiving gas directly from the combination controlvalve 22 and one burner 20 receiving gas through the shutoff valve 42. Auser enters a temperature, the set temperature, to the controller 16 byusing the user interface 12. The controller 16 compares the settemperature with the measured temperature, supplied by the operatingparameter sensor 14. If the measured temperature is above the settemperature, the controller 16 may close the combination control valve22, thereby shutting off the flow of gas to the shutoff valve 42, andthe burners 20.

If the measured temperature is below the set temperature, the controller16 may send a signal to the combination control valve 22 to open toallow some gas to flow to the burners 20, where it may be combusted andproduce heat. If the measured temperature is well below the settemperature, the controller 16 may leave the combination control valve22 open and send a signal to the shutoff valve 42 to open and allow gasflow to its connected burner 20. As the measured temperature approachesthe set temperature, the controller 16 may send a signal to the shutoffvalve 42 to close again.

If the measured temperature equals the set temperature, the controller16 may send a signal to the combination control valve 22 to openperiodically. The controller 16 may maintain this setting, or may adjustthe setting slightly, as long as the two temperatures are equal. If themeasured temperature increases or decreases, the controller 16 may openor close the combination control valve 22 and the shutoff valve 42accordingly, as described above.

The variable output heating control system 10 is disclosed primarily foruse with a residential or commercial gas furnace. However, theprinciples of the invention disclosed herein may also be used with awater heater, a boiler, a hot water tank, an oil furnace, a gasfireplace, a residential gas oven, a commercial gas oven, a gas grill, agas clothes dryer, a gas agricultural grain dryer, a materialsprocessor, a materials dryer, a process dryer, a thermal processor, afluids processor, a chemicals processor, or other systems or devicesrequiring a controlled, variable output heat source.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

1. A heating control system, the system comprising: a controlleroperable to receive a set temperature and a measured temperature and togenerate a plurality of gas flow control commands, including an offcommand, an on command and an additional plurality of gas flow controlcommands in the on position; a modulating combination control valveoperable to vary the flow of gas from an external gas source based on agas flow control command from the controller; a plurality of shutoffvalves operable to shut off the flow of gas received from the modulatingcombination control valve based on a gas flow control command from thecontroller, wherein each shutoff valve may be shut off separately; and aplurality of burners operable to provide heat corresponding to thecombustion of gas received from the modulating combination control valveand the plurality of shutoff valves.
 2. The system of claim 1, furtherincluding a user interface coupled with the controller for a user toenter operating parameters, including the set temperature.
 3. The systemof claim 1, further including at least one operating parameter sensorcoupled with the controller operable to provide the measured temperatureand other operating parameters.
 4. The system of claim 1, wherein thecontroller generates a command to increase the flow of gas if themeasured temperature is less than the set temperature.
 5. The system ofclaim 1, wherein the controller generates a command to decrease the flowof gas if the measured temperature is greater than the set temperature.6. The system of claim 1, wherein the controller generates a command toshut off at least one shutoff valve if the measured temperature isgreater than the set temperature.
 7. The system of claim 1, wherein thecontroller generates a command to open at least one shutoff valve if themeasured temperature is less than the set temperature.
 8. The system ofclaim 1, wherein the plurality of shutoff valves and the plurality ofburners are operably coupled in a one to one ratio.
 9. The system ofclaim 1, wherein at least a portion of the burners receives gas from oneshutoff valve.
 10. A heating control system, the system comprising: acontroller operable to receive a set temperature and a measuredtemperature and to generate a plurality of gas flow control commands,including an off command, an on command and an additional plurality ofgas flow control commands in the on position; a combination controlvalve operable to control flow of gas from an external gas source basedon a gas flow control command from the controller; at least one shutoffvalve operable to shut off the flow of gas received from the combinationcontrol valve based on a gas flow control command from the controller,wherein each shutoff valve may be shut off separately; and a pluralityof burners operable to provide heat corresponding to the combustion ofgas received from the combination control valve and the at least oneshutoff valve.
 11. The system of claim 10, further including a userinterface coupled with the controller for a user to enter the settemperature.
 12. The system of claim 10, further including at least oneoperating parameter sensor coupled with the controller operable toprovide the measured temperature.
 13. The system of claim 10, furtherincluding a plurality of shutoff valves.
 14. A method for controllingthe heat output of a combustible fuel heating system, the methodcomprising the steps of a controller: a) receiving a set temperaturefrom a user; b) receiving a measured temperature from at least oneoperating parameter sensor; c) comparing the measured temperature andthe set temperature; d) for the measured temperature above the settemperature; e) issuing a command to a modulating combination controlvalve to decrease the flow of gas through a plurality of shutoff valvescoupled to a plurality of burners; f) issuing a command to close one ormore of the plurality of shutoff valves; g) for the measured temperaturebelow the set temperature; h) issuing a command to a modulatingcombination control valve to increase the flow of gas through aplurality of shutoff valves coupled to a plurality of burners; i)issuing a command to open one or more of the plurality of shutoffvalves; and j) for a measured temperature that is equal to the settemperature issuing a command to the modulating combination controlvalve to maintain the rate of flow of gas.